1. Technical Field
The present disclosure relates to systems and methods for monitoring the work flow of a resource.
2. Description of the Related Art
Manufacturing costs represent a large portion of the cost to assemble products for eventual sale. However, such manufacturing costs can be greatly reduced by proper work flow management.
Work flow management, however, typically requires monitoring of the work process itself. Such data not only provides statistical data regarding the assembly process itself (data that can be used to formulate new work flows and processes), it can also provide data that can be used in the assembly process itself. For example, if its known that an assembly has just passed a particular assembly station, that information can be used to begin a process that must be completed before the assembly proceeds to a subsequent assembly station.
The location of assemblies and parts can be determined using commercially available wireless identification system such as radio frequency identification (RFID) systems. Radio Frequency Identification (RFID) is an automatic identification method that stores and remotely retrieves data using devices called RFID tags or transponders. An RFID tag can be attached to or incorporated into the assembly or part, and can be used to identify the subject using radio waves. Chip-based RFID tags contain silicon chips and antennas. Tags include passive tags, which require no internal power supply, and active tags, which require a power source.
Active tags work relatively well when they are within the line of sight of three or more location receivers. Problems occur when an active tag is surrounded by metal objects and the radio transmissions travel through indirect paths before they are received. Under these conditions, signal reflect against intermediary objects which may serve as primary signals, and/or multiple signal paths (multipaths) distorting the time of arrival to the receivers. This alteration causes inaccuracies in receiving and time stamping the signals used in the calculation of the location coordinates.
Commercially available active radio identification systems provide location signals for triangulation ranging between 5 feet to 100 feet from the true location. This level of accuracy is acceptable in the environments where approximation is possible and not critical to a decision process.
However, in many manufacturing facilities, the accuracy provided by commercially available RFID system may be insufficient due to the close proximity of location boundaries. When the accuracy problem exceeds the assigned location boundary (i.e. aircraft position, work cell, stock room, etc), the reported location is constrained and inaccurate. This not only affects the system's ability to determine which area the assembly is located, it also affects the gathering of statistics regarding how long the assembly remained in that area. That is because any data regarding how long an assembly was in any particular work cell is typically reset when the assembly leaves the cell.
The foregoing problems may be ameliorated by increasing the accuracy of the RFID system, but in the multipath environment described above, this can be prohibitively expensive or impossible
What is needed is a system and method that provides sufficiently accurate and reliable information as to the location status of assemblies, yet does so using commercially available RFID systems. The present invention satisfies that need.